Is MS SQL Server 2017 Supported as Data source?

1. The Appian documentation may not mention it as supported - but that does not mean that it wont work.
2. Appian uses JDBC connectors to connect to the RDBMS.
3. So - as long as the JDBC jar is compatible with MS SQL Server 2017 , it will work.
4. The documentation mentions that MS SQL Server 2016 is supported - so just check if the JDBC jar which Appian installation has - is it compatible with MS SQL Server 2017. You may request the admin to replace the JDBC jar and update the config file.
5. As per Microsoft SQL server documentation you need Microsoft JDBC Driver 6.4 for SQL Server.

6. version 6.2 and 6.4 both should be fine for connecting to SQL Server 2017 https://docs.microsoft.com/en-us/sql/connect/jdbc/microsoft-jdbc-driver-for-sql-server-support-matrix?view=sql-server-2017 

chetany 

I agree with you suspicion that this version of SQL server will probably work just fine.

However, for the sake of our friends here on community, it's important to point out that JDBC connectivity is not the only criteria considered for Appian to offer official support for a database.
For example, DB2 running on z/OS is JDBC compatible, but it's not supported.

When using queryEntities (a!queryEntity), or writeToDataStore smart services you're not writing the SQL. Appian's data layer governs the syntax for those commands in a precise and reliable manner. This means that Appian has to know exactly what type of database it's talking to.  Subtle nuances in acceptable syntax must be accounted for.   Hence, the point made by ericg329 regarding Appian Product/QA sign off is very important to consider.   The product team needs to account for Appian to prepare the correct SQL for the appropriate database.

If you choose to configure an unsupported database, you are accepting the risk of encountering unexpected behavior.

 My recommendation to siddharths would be to avoid using an unsupported database as a business data source. 
Definitely do not use an unsupported database for primary.

chetany 

I agree with you suspicion that this version of SQL server will probably work just fine.

However, for the sake of our friends here on community, it's important to point out that JDBC connectivity is not the only criteria considered for Appian to offer official support for a database.
For example, DB2 running on z/OS is JDBC compatible, but it's not supported.

When using queryEntities (a!queryEntity), or writeToDataStore smart services you're not writing the SQL. Appian's data layer governs the syntax for those commands in a precise and reliable manner. This means that Appian has to know exactly what type of database it's talking to.  Subtle nuances in acceptable syntax must be accounted for.   Hence, the point made by ericg329 regarding Appian Product/QA sign off is very important to consider.   The product team needs to account for Appian to prepare the correct SQL for the appropriate database.

If you choose to configure an unsupported database, you are accepting the risk of encountering unexpected behavior.

 My recommendation to siddharths would be to avoid using an unsupported database as a business data source. 
Definitely do not use an unsupported database for primary.